Bus behavior is the electrical and timing rules that determine how a computer and an attached device communicate over a shared interface. It includes signal voltages, when signals are sent and sampled, how devices request access, and how they respond to reads or writes. A cartridge or expansion card must follow these rules so the host can recognize it and exchange data reliably.
In security, the bus is a physical trust boundary: connected hardware can interact with the host through the access the interface provides. Unexpected signals or poorly implemented timing may cause instability, expose data, or create opportunities for malicious behavior, depending on the system. In older computers such as MSX systems, compatible cartridges should match documented electrical and timing requirements. For modern devices, defenses include validating peripherals, limiting interface access, and testing hardware across host revisions.